The problem exists with prior brakes of allowing the main shaft to turn slowly forwards and backwards for elimination of the trouble which has triggered the braking. This is difficult because the sliding travel of the pressure-piece between its two extreme positions is dimensioned very closely in order to be able to start the braking as fast as possible without delay, that is, often so closely that simultaneous touching by the friction surfaces of the drive coupling counterpart and of the brake stator is not always excluded with certainty. However, rubbing of the pressure-piece on the brake stator results in energy loss, heating and wear.
In practice, the pressure-piece is moved alternately and briefly with light pressure between its two extreme positions, which causes a jerky turning and stopping of the main shaft. But this method is not satisfactory since on the one hand the power requirement of the loom around one revolution of the main shaft is variable, so that the turning and stopping motion becomes uncontrollabe, and on the other hand the alternating contact of the pressure-piece with the friction surfaces, accompanied by slip, brings about heating and wear.
The invention has in view the elimination of these disadvantages. It consists in the brake being made releasable without alteration of the position of the pressure-piece. In other words, the friction surfaces of the brake are connected releasably to their mounting so that release can be effected under control.